In general, a memory system includes a memory device for storing data and a host for controlling operations of the memory device. The memory device is classified into a volatile memory (such as DRAM, SRAM, and so forth) and a non-volatile memory (such as EEPROM, FRAM, PRAM, MRAM, flash memory, and so forth).
The volatile memory loses its stored data when power supply is cut off, but the non-volatile memory retains its stored data even when there is no power supply. Among non-volatile memories, the flash memory is widely used as a data storage medium because of advantages such as a high programming speed, lower power consumption, high capacity data storage, and so forth.
A memory device demanding a high degree of integration causes defective products because of a plurality of limited requirements in manufacturing processes. Various trials have been made in order to resolve yield decrease and defects, which are caused by the factors such as the high degree of integration of a memory device. However, if a memory device is mounted in a memory system and is in operation, it is difficult for a user to determine defectiveness of a memory device.
A high capacity storage device such as a flash memory card or a solid state disk (SSD) has a typical structure including a plurality of flash memory chips. In general, the SSD is designed to replace a hard disk drive, and therefore, has a significantly larger capacity than a memory card. For example, the SSD may have one or two orders of magnitude greater storage space. Accordingly, the SSD includes many more flash memory chips than a memory card. In some flash memory chips, if the number of bad blocks is drastically increased due to program/erase fails and pre-reserved replacement blocks are all consumed, no more service is available.
A semiconductor memory device is a memory device capable of reading data when necessary after storing the data. The semiconductor memory device is largely classified into a random access memory (RAM) and a read only memory (ROM). Data stored in the RAM disappears when power supply is cut off. This type of a memory is called a volatile memory. On the contrary, data stored in the ROM does not disappear even when there is no power supply. This type of a memory is called a non-volatile memory.
A kind of the non-volatile memory device includes a flash memory device. The flash memory device is largely classified into a NOR type and a NAND type. Recently, portable electronic devices such as digital cameras, MP3 players, mobile phones, PDAs, and so forth use flash memories. This is because the flash memory is a non-volatile device having characteristics such as low power consumption and the high degree of integration. Because the flash memory is used in the portable electronic device, the reliability and life cycle of the flash memory are closely related to those of the portable electronic device. Accordingly, it is desirable to improve the reliability and life cycle of the flash memory.
Other specific volatile memory devices include SRAM, DRAM, and SDRAM. Other non-volatile memory devices include ROM, PROM, EPROM, EEPROM, PRAM, MRAM, RRAM, and FRAM.
Lately, a semiconductor disk device using a semiconductor memory device has been developed. The semiconductor disk device is better than a hard disk using a rotational disk, in aspects of reliability and speed. Accordingly, a computing system using the semiconductor disk device instead of a hard disk as a storage device has been developed.